U.S. patent application number 10/714394 was filed with the patent office on 2004-10-07 for electrode structure for polymer electrolyte fuel cells, and polymer electrolyte fuel cell using the same.
Invention is credited to Iguchi, Masaru, Kaji, Hayato, Kanaoka, Nagayuki, Mitsuta, Naoki, Morikawa, Hiroshi, Sohma, Hiroshi.
Application Number | 20040197632 10/714394 |
Document ID | / |
Family ID | 32179162 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040197632 |
Kind Code |
A1 |
Sohma, Hiroshi ; et
al. |
October 7, 2004 |
Electrode structure for polymer electrolyte fuel cells, and polymer
electrolyte fuel cell using the same
Abstract
The present invention provides an electrode structure for
polymer electrolyte fuel cells, inexpensive, and exhibiting
excellent power production capacity and durability even under high
temperature/low humidity conditions, and also provides a polymer
electrolyte fuel cell which incorporates the same electrode
structure. The present invention also provides an electrical device
and transportation device, each incorporating the same polymer
electrolyte fuel cell. The electrode structure comprises a pair of
electrode catalyst layers 1,1, each containing a catalyst supported
by carbon particles, and polymer electrolyte membrane 2 placed
between these electrode catalyst layers 1,1. The polymer
electrolyte membrane 2 is of a sulfonated polyarylene composed of
0.5 to 100% by mol of the first repeating unit represented by the
general formula (1) and 0 to 99.5% by mol of the second repeating
unit represented by the general formula (2): 1 (wherein, A is a
divalent organic group; and a benzene ring includes its
derivative), 2 (wherein, --W-- is a divalent electron attracting
group; --T-- is a divalent organic group; and R.sup.1 to R.sup.8
are a hydrogen atom or fluorine atom, an alkyl group,
fluorine-substituted alkyl group, allyl group, aryl group or cyano
group, and may be the same or different).
Inventors: |
Sohma, Hiroshi; (Saitama,
JP) ; Iguchi, Masaru; (Saitama, JP) ; Kanaoka,
Nagayuki; (Saitama, JP) ; Kaji, Hayato;
(Saitama, JP) ; Morikawa, Hiroshi; (Saitama,
JP) ; Mitsuta, Naoki; (Saitama, JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN
1050 CONNECTICUT AVENUE, N.W.
SUITE 400
WASHINGTON
DC
20036
US
|
Family ID: |
32179162 |
Appl. No.: |
10/714394 |
Filed: |
November 17, 2003 |
Current U.S.
Class: |
429/480 ;
429/482; 429/494 |
Current CPC
Class: |
C08L 65/00 20130101;
C08G 65/4056 20130101; H01M 8/1039 20130101; C08G 2650/64 20130101;
C08L 71/00 20130101; H01M 8/1025 20130101; H01M 2008/1095 20130101;
Y02E 60/50 20130101; H01M 4/8605 20130101; H01M 2300/0082 20130101;
H01M 8/1004 20130101; H01M 4/926 20130101; C08G 65/4025 20130101;
C08L 65/00 20130101; C08L 2666/22 20130101 |
Class at
Publication: |
429/033 ;
429/044 |
International
Class: |
H01M 008/10; H01M
004/96 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 18, 2002 |
JP |
2002-333143 |
Oct 30, 2003 |
JP |
2003-371047 |
Claims
What is claimed is:
1. An electrode structure for polymer electrolyte fuel cells,
comprising a pair of electrode catalyst layers, each containing a
catalyst supported by carbon particles, and a polymer electrolyte
membrane placed between the electrode catalyst layers, wherein the
polymer electrolyte membrane is formed from a sulfonated
polyarylene consisting of 0.5 to 100% by mol of a first repeating
unit represented by the general formula (1) and 0 to 99.5% by mol
of a second repeating unit represented by the general formula (2):
29(wherein, A is a divalent organic group; and a benzene ring
includes its derivative), 30(wherein, --W-- is a divalent electron
attracting group; --T-- is a divalent organic group; and R.sup.1 to
R.sup.8 are a hydrogen atom or fluorine atom, an alkyl group,
fluorine-substituted alkyl group, allyl group, aryl group or cyano
group, and may be the same or different).
2. The electrode structure for polymer electrolyte fuel cells
according to claim 1, wherein said electrode catalyst layer
contains a noble metal catalyst at 0.1 to 1.0 mg/cm.sup.2, and said
carbon particles have an average diameter of 10 to 100 nm.
3. The electrode structure for polymer electrolyte fuel cells
according to claim 1, wherein said polymer electrolyte membrane is
composed of a sulfonated polyarylene represented by the general
formula (3): 31
4. The electrode structure for polymer electrolyte fuel cells
according to claim 1, wherein said electrode catalyst layers
comprise an electrode diffusion layer.
5. A polymer electrolyte fuel cell comprising an electrode
structure for polymer electrolyte fuel cells, which comprises a
pair of electrode catalyst layers, each containing a catalyst
supported by carbon particles, and a polymer electrolyte membrane
placed between these electrode catalyst layers, the polymer
electrolyte membrane being formed by a sulfonated polyarylene as a
copolymer consisting of 0.5 to 100% by mol of a first repeating
unit represented by the general formula (1) and 0 to 99.5% by mol
of a second repeating unit represented by the general formula (2):
32(wherein, A is a divalent organic group; and a benzene ring
includes its derivative), 33(wherein, --W-- is a divalent electron
attracting group; --T-- is a divalent organic group; and R.sup.1 to
R.sup.8 are a hydrogen atom or fluorine atom, an alkyl group,
fluorine-substituted alkyl group, allyl group, aryl group or cyano
group, and may be the same or different), wherein a fuel gas is
supplied to one of the electrode catalyst layers and an oxidizing
gas is supplied to the other electrode catalyst layer.
6. An electrical device which uses a polymer electrolyte fuel cell
comprising an electrode structure for polymer electrolyte fuel
cells, which comprises a pair of electrode catalyst layers, each
containing a catalyst supported by carbon particles, and a polymer
electrolyte membrane placed between these electrode catalyst
layers, the polymer electrolyte membrane being formed by of a
sulfonated polyarylene as a copolymer consisting of 0.5 to 100% by
mol of a first repeating unit represented by the general formula
(1) and 0 to 99.5% by mol of a second repeating unit represented by
the general formula (2): 34(wherein, A is a divalent organic group;
and a benzene ring includes its derivative), 35(wherein, --W-- is a
divalent electron attracting group; --T-- is a divalent organic
group; and R.sup.1 to R.sup.8 are a hydrogen atom or fluorine atom,
an alkyl group, fluorine-substituted alkyl group, allyl group, aryl
group or cyano group, and may be the same or different), and a fuel
gas is supplied to one of the electrode catalyst layers and an
oxidizing gas is supplied to the other electrode catalyst
layer.
7. A transportation device which uses a polymer electrolyte fuel
cell comprising an electrode structure for polymer electrolyte fuel
cells, which comprises a pair of electrode catalyst layers, each
containing a catalyst supported by carbon particles, and a polymer
electrolyte membrane placed between these electrode catalyst
layers, the polymer electrolyte membrane being formed by a
sulfonated polyarylene as a copolymer composed of 0.5 to 100% by
mol of a first repeating unit represented by the general formula
(1) and 0 to 99.5% by mol of a second repeating unit represented by
the general formula (2): 36(wherein, A is a divalent organic group;
and a benzene ring includes its derivative), 37(wherein, --W-- is a
divalent electron attracting group; --T-- is a divalent organic
group; and R.sup.1 to R.sup.8 are a hydrogen atom or fluorine atom,
an alkyl group, fluorine-substituted alkyl group, allyl group, aryl
group or cyano group, and may be the same or different), and a fuel
gas is supplied to one of the electrode catalyst layers and an
oxidizing gas is supplied to the other electrode catalyst layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electrode structure for
polymer electrolyte fuel cells, and polymer electrolyte fuel cell
using the same.
[0003] 2. Description of the Related Art
[0004] The environmental problems, e.g., global warming, resulting
from consumption of fossil fuels are becoming more serious, while
oil resources are being depleted. Therefore, fuel cells have been
attracting attention as clean power sources for motors, which
release no carbon dioxide. They have been extensively developed,
and commercialized in some areas. When a fuel cell is mounted in an
automobile or the like, a polymer electrolyte fuel cell including a
polymer electrolyte membrane is suitably used, because of its
capacity to produce a high voltage and large electric current.
[0005] As an electrode structures for polymer electrolyte fuel
cell, one comprising a pair of electrode catalyst layers composed
of a catalyst of platinum or the like supported by a catalyst
carrier of carbon black or the like and monolithically formed by an
ion-conductive polymer binder, and an ion-conductive polymer
electrolyte membrane placed between these electrode catalyst layers
in which each electrode catalyst layer is coated with a diffusion
layer (see, e.g., by Japanese Patent Laid-Open No. 2000-223136).
The electrode structure constitutes a polymer electrolyte fuel cell
with a separator, which also works as a gas passage, laminated on
each of the electrode catalyst layers.
[0006] In the polymer electrolyte fuel cell, a reducing gas, e.g.,
hydrogen or methanol, is introduced into one electrode catalyst
layer working as the fuel electrode via the diffusion layer, and an
oxidizing gas, e.g., air or oxygen, is introduced into the other
electrode catalyst layer working as the oxygen electrode also via
the diffusion layer. This structure produces proton from the
reducing gas on the fuel electrode by the actions of the catalyst
in the electrode catalyst layer. The proton moves towards the
electrode catalyst layer on the oxygen electrode side via the
polymer electrolyte membrane, to react with the oxidizing gas
introduced on the oxygen electrode to produce water in the
electrode catalyst layer on the oxygen electrode side by the
actions of the catalyst contained in the catalyst layer. Therefore,
a current can be produced by connecting the fuel electrode and
oxygen electrode to each other by a cable.
[0007] For the polymer electrolyte membrane in the electrode
structure, perfluoroalkylenesulfonic acid polymer compounds (e.g.,
Du Pont's Nafion (trade name)) have been widely used. The
perfluoroalkylenesulfonic acid polymer compound exhibits good
proton conductivity and chemical resistance as a fluorine-based
resin, because it is sulfonated.
[0008] However, perfluoroalkylenesulfonic acid polymer compound
involves some disadvantages. It is very expensive, and low in creep
resistance at high temperature and hence difficult to stably retain
its shape. Another disadvantage results from its high gas
permeability, which may deteriorate its durability, in particular
under high temperature/low humidity conditions, because oxygen may
cross-leaks from the cathode side to react in the vicinity of the
catalyst on the anode side to produce hydrogen peroxide as a
by-product, which will accelerate deterioration of the
membrane.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide an
electrode structure for polymer electrolyte fuel cells, which is
inexpensive, and exhibits excellent power production capacity and
durability even under high temperature/low humidity conditions by
solving the above problems.
[0010] It is another object of the present invention to provide a
polymer electrolyte fuel cell using the same electrode
structure.
[0011] An electrode structure for polymer electrolyte fuel cells
may be composed of a hydrocarbon-based polymer or the like, in
place of the perfluoroalkylenesulfonic acid polymer compound, as a
less expensive ion-conductive material. The hydrocarbon-based
polymer has high gas barrier property and creep-resistant, that is
to say it has low gas permeability and high shape stability.
[0012] The inventors of the present invention have found, after
having extensively screened a variety of hydrocarbon-based
polymers, that an electrode structure for polymer electrolyte fuel
cells can exhibit excellent power production capacity and
durability even under high temperature/low humidity conditions,
when it is composed of a specific sulfonated polyarylene as the
ion-conductive material, achieving the present invention.
[0013] The present invention provides an electrode structure for
polymer electrolyte fuel cells, comprising a pair of electrode
catalyst layers, each containing a catalyst supported by carbon
particles, and a polymer electrolyte membrane placed between these
electrode catalyst layers, wherein the polymer electrolyte membrane
is formed from a sulfonated polyarylene consisting of 0.5 to 100%
by mol of a first repeating unit represented by the general formula
(1) and 0 to 99.5% by mol of a second repeating unit represented by
the general formula (2): 3
[0014] (wherein, A is a divalent organic group; and a benzene ring
includes its derivative), 4
[0015] (wherein, --W-- is a divalent electron attracting group;
--T-- is a divalent organic group; and R.sup.1 to R.sup.8 are a
hydrogen atom or fluorine atom, an alkyl group,
fluorine-substituted alkyl group, allyl group, aryl group or cyano
group, and may be the same or different).
[0016] Examples of the divalent organic group include electron
attracting groups, e.g., --CO--, --CONH--, --(CF.sub.2).sub.p--
("p" is an integer of 1 to 10), --C(CF.sub.3).sub.2--, --COO--,
--SO-- and --SO.sub.2--; groups such as --O--, --S--, --CH.dbd.CH--
and --C.ident.C--; and electron donating groups represented by the
following formula: 5
[0017] Examples of the divalent electron attracting group include
--CO--, --CONH--, --(CF.sub.2).sub.p-- ("p" is an integer of 1 to
10), --C(CF.sub.3).sub.2--, --COO--, --SO-- and --SO.sub.2--.
[0018] The sulfonated polyarylene can be prepared by
copolymerization of 0.5 to 100% by mol of the first component
represented by the general formula (1') with 0 to 99.5% by mol of
the second component represented by the general formula (2'), and
then hydrolyzing the sulfonic acid ester group (--SO.sub.3R). 6
[0019] (wherein, A is a divalent organic group; and a benzene ring
includes its derivative), 7
[0020] (wherein, --W-- is a divalent electron attracting group;
--T-- is a divalent organic group; and R.sup.1 to R.sup.8 are a
hydrogen atom or fluorine atom, an alkyl group,
fluorine-substituted alkyl group, allyl group, aryl group or cyano
group, and may be the same or different).
[0021] The divalent organic group and divalent electron attracting
group are the same as those in the general formula (1) or (2).
[0022] In the general formula (1'), X is a halogen atom (chlorine,
bromine or iodine) except fluorine, or an atom or a group selected
from the group consisting of --OSO.sub.3CH.sub.3 and
--OSO.sub.3CF.sub.3; and R is a hydrocarbon group of 4 to 20 carbon
atoms. In the general formula (2'), R' and R" which may be the same
or different are a halogen atom except fluorine or a group selected
from the group consisting of --OSO.sub.2Z (Z is an alkyl,
fluorine-substituted alkyl or aryl group).
[0023] In the electrode structure for polymer electrolyte fuel cell
of the present invention, the sulfonated polyarylene for the
polymer electrolyte membrane is a sulfonated hydrocarbon-based
polymer, and hence is inexpensive and gives a good power production
capacity. The sulfonated polyarylene as a sulfonated
hydrocarbon-based polymer exhibits higher gas barrier property than
perfluoroalkylenesulfonic acid polymer compound, and thus prevents
production of hydrogen peroxide in the vicinity of the catalyst on
the electrode more efficiently and exhibits higher durability under
high temperature/low humidity conditions.
[0024] On the other hand, a sulfonated polyarylene produced by
sulfonating polymerized polyarylene to introduce sulfonic group in
the benzene ring tends to suffer elimination of the sulfonic group
from the benzene ring. Therefore, such a sulfonated polyarylene
needs to have higher sulfonating equivalents to secure a required
ion-exchanging capacity. However, the sulfonated polyarylene tends
to have the sulfonic group and oxy group (--O--) working as the
crosslinking points under high temperature/low humidity conditions
to produce insoluble components by the inter-molecular crosslinking
reactions. This tendency is more noted as it has higher sulfonating
equivalents. As a result, it loses toughness and difficult to
secure sufficient durability.
[0025] In contrast, the sulfonated polyarylene used in the present
invention is produced by copolymerization of the first component
represented by the general formula (1') with the second component
represented by the general formula (2'), and then hydrolyzing the
--SO.sub.3R group into sulfonic group (--SO.sub.3H) The first
component represented by the general formula (1') already has the
--SO.sub.3R group bound to the benzene ring, and the sulfonic group
as the hydrolyzing product of the --SO.sub.3R group will not be
easily eliminated from the benzene ring. Therefore, the sulfonated
polyarylene for the present invention can have lower sulfonating
equivalents to secure a required ion-exchanging capacity. Moreover,
the sulfonated polyarylene for the present invention has no oxy
group, potentially providing a crosslinking point, in the molecular
structure, which reduces production of the insoluble components by
the inter-molecular crosslinking between the sulfonated polyarylene
molecules under high temperature/low humidity conditions, and is
advantageous for securing good durability.
[0026] As a result, the electrode structure of the present
invention for polymer electrolyte fuel cells can exhibit excellent
power production capacity and durability even under high
temperature/low humidity conditions.
[0027] The "sulfonated polyarylene" described in this specification
means a sulfonated polymer having the following structure: 8
[0028] (wherein, --X-- is a single bond or a divalent organic
group; --W-- is a divalent electron attracting group; --T-- is a
divalent organic group; R.sup.1 to R.sup.8 are a hydrogen atom or
fluorine atom, an alkyl group, allyl group, allyl group or cyano
group, and may be the same or different; "p" is 0.5 to 100; "q" is
99.5 to 0; "r" is an integer of 0 to 10; and "s" is an integer of 1
to 100).
[0029] The divalent organic group and divalent electron attracting
group are the same as those for the general formula (1) or (2).
[0030] The electrode structure for polymer electrolyte fuel cells
includes the sulfonated polyarylene for the polymer electrolyte
membrane, and the electrode catalyst layer containing a noble metal
catalyst at 0.1 to 1.0 mg/cm.sup.2, exhibiting an excellent power
production capacity, because the carbon particles supporting the
catalyst have an average size of 10 to 100 nm. Examples of the
noble metal catalyst are those of platinum, rhodium and
platinum-rhodium.
[0031] The electrode structure for polymer electrolyte fuel cell of
the present invention may not exhibit a sufficient power production
capacity, when the amount of the noble metal catalyst contained in
the polymer electrolyte membrane as a catalyst is below
0.1mg/cm.sup.2. At above 1.0mg/cm.sup.2, on the other hand, it may
not only exhibit an insufficient power production capacity
conversely but also is economically disadvantageous because of
increased cost.
[0032] Moreover, it may not exhibit a sufficient power production
capacity, when the carbon particles supporting the noble metal
catalyst particles have an average size of below 10 nm, because of
lowered dispersibility of the catalyst particles. On the other
hand, the average particle diameter exceeding 100 nm also may make
the electrode structure insufficient in power production capacity,
because of an excessive activation overvoltage possibly
occurring.
[0033] More specifically, the sulfonated polyarylenes for the
polymer electrolyte membrane include the polymer represented by the
general formula (3): 9
[0034] The electrode structure for polymer electrolyte fuel cell of
the present invention comprises an electrode diffusion layer on the
electrode catalyst layers, whereby the fuel gas supplied being
guided to the electrode catalyst layers via the electrode diffusion
layer on one side, and the oxidizing gas supplied being guided to
the electrode catalyst layer also via the electrode diffusion layer
on the other side.
[0035] The electrode structure for polymer electrolyte fuel cell of
the present invention can work as a polymer electrolyte fuel cell
by supplying the fuel gas to one of the electrode catalyst layers
and the oxidizing gas to the other electrode catalyst layer.
[0036] The polymer electrolyte fuel cell which includes the
electrode structure for polymer electrolyte fuel cell of the
present invention can be employed as a power source, back-up power
source or the like for electric/electronic devices, e.g., personal
computers and cellular phones. It is also serviceable as a power
source for transportation devices, e.g., automobiles and ships
(e.g., submarines).
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is an illustrative cross-section of one embodiment of
the electrode structure, prepared in Example 1;
[0038] FIG. 2 shows power generation capacity of the electrode
structure; and
[0039] FIG. 3 also shows power generation capacity of the electrode
structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] One of the preferred embodiments of the present invention is
described in more detail by referring to the attached drawings.
[0041] Referring to FIG. 1, the preferred embodiment of the
electrode structure is comprising a pair of the electrode catalyst
layers 1,1, polymer electrolyte membrane 2 sandwiched between these
electrode catalyst layers 1,1, and diffusion layers 3,3, each
laminated on each electrode catalyst layer.
[0042] The electrode catalyst layer 1 is composed of catalyst
particles and ion-conductive binder, wherein platinum particles are
for example included as the catalyst at 0.1 to 1.0 mg/cm.sup.2. The
catalyst particles are noble metal catalyst particles such as the
platinum particles supported by carbon particles, e.g., those of
carbon black (furnace black), and have an average particle diameter
of 10 to 100nm. The platinum particle/carbon particle weigh ratio
is set at, e.g., platinum particle:carbon particle=1:1. A polymer
electrolyte, e.g., perfluoroalkylenesulfonic acid compound (e.g.,
Du Pont's Nafion (trade name)) or sulfonated polyarylene-based
polymer, is used for the ion-conductive binder.
[0043] The polymer electrolyte membrane 2 is formed by the
sulfonated polyarylene consisting of the first repeating unit
represented by the general formula (1) and second repeating unit
represented by the general formula (2): 10
[0044] (wherein, A is a divalent organic group; and a benzene ring
includes its derivative), 11
[0045] (wherein, --W-- is a divalent electron attracting group;
--T-- is a divalent organic group; and R.sup.1 to R.sup.8 are a
hydrogen atom or fluorine atom, an alkyl group,
fluorine-substituted alkyl group, allyl group, aryl group or cyano
group, and may be the same or different).
[0046] Examples of the divalent organic group include electron
attracting groups, e.g., --CO--, --CONH--, --(CF.sub.2).sub.p--
("p" is an integer of 1 to 10), --C(CF.sub.3).sub.2--, --COO--,
--SO-- and --SO.sub.2--; groups such as --O--, --S--, --CH.dbd.CH--
and --C.ident.C--; and electron donating groups represented by the
following formula: 12
[0047] Examples of the divalent electron attracting group include
--CO--, --CONH--, --(CF.sub.2).sub.p-- ("p" is an integer of 1 to
10), --C(CF.sub.3).sub.2--, --COO--, --SO-- and --SO.sub.2--.
[0048] The electron attracting group is a divalent group having a
Hammet substituent constant of 0.06 or more at the meta-site of a
phenyl group and 0.01 or more at the para-site of a phenyl
group.
[0049] The derivatives of benzene ring include a phenylene group
having at least one substituent selected from the group consisting
of a fluorine atom, and an alkyl group, fluorine-substituted alkyl
group, allyl group and aryl group. When it has 2 or more
substituents, they may be the same or different.
[0050] Examples of the alkyl group include a methyl group, ethyl
group, propyl group, butyl group, amyl group and hexyl group, of
which methyl group and ethyl group are more preferable.
[0051] Examples of the fluorine-substituted alkyl group include a
trifluoromethyl group, perfluoroethyl group, perfluoropropyl group,
perfluorobutyl group, perfluoropentyl group and perfluorohexyl
group, of which a trifluoromethyl group and perfluoroethyl group
are more preferable.
[0052] Examples of the allyl group include a propenyl group, and
those of the aryl group include a phenyl group and
pentafluorophenyl group.
[0053] In the general formula (2), "1" is a positive integer, upper
limit of which is normally 100, preferably 80.
[0054] The sulfonated polyarylene may consist only of the first
repeating unit represented by the general formula (1), but
preferably has the second repeating unit represented by the general
formula (2) additionally, to improve toughness of the polymer
electrolyte membrane. It preferably consists of 0.5 to 99.999% by
mol of the first repeating unit and 0.001 to 99.5% by mol of the
second repeating unit.
[0055] The sulfonated polyarylene can be prepared by
copolymerization of 0.5 to 100% by mol, preferably 0.5 to 99.999%
by mol, of the first component represented by the general formula
(1') with 0 to 99.5% by mol, preferably 0.001 to 99.5% by mol, of
the second component represented by the general formula (2'), and
then hydrolyzing the sulfonic acid ester group (--SO.sub.3R) 13
[0056] (wherein, A is a divalent organic group; and a benzene ring
includes its derivative), 14
[0057] (wherein, --W-- is a divalent electron attracting group;
--T-- is a divalent organic group; and R.sup.1 to R.sup.8 are a
hydrogen atom or fluorine atom, an alkyl group,
fluorine-substituted alkyl group, allyl group, aryl group or cyano
group, and may be the same or different).
[0058] The electron attracting group, electron donating group and
derivative of benzene ring is the same as those in the general
formula (1) or (2).
[0059] In the general formula (1'), X is a halogen atom (chlorine,
bromine or iodine) except fluorine, or an atom or a group selected
from the group consisting of --OSO.sub.3CH.sub.3 and
--OSO.sub.3CF.sub.3; and R is a hydrocarbon group of 4 to 20 carbon
atoms, more specifically, tert-butyl group, iso-butyl group,
n-butyl group, sec-butyl group, neopentyl group and cyclopentyl
group or the like.
[0060] In the general formula (2'), R' and R" are each a halogen
atom except fluorine or a group selected from the group consisting
of --OSO.sub.2Z (Z is analkyl group, fluorine-substituted alkyl
group or aryl group). The alkyl group represented by Z includes
methyl group and ethyl group; fluorine-substituted alkyl groups
includes trifluoromethyl group; and aryl groups includes phenyl
group and p-tolyl group. In the general formula (2'), "1" is a
positive integer, upper limit of which is normally 100, preferably
80.
[0061] The first component may be copolymerized with the second
component in the presence of a catalyst system containing a
transition metal compound. The catalyst system is composed of a
transition metal salt, a compound as a ligand and a reducing agent,
or a transition metal complex (including copper salt) and a
reducing agent, the former having a coordinated ligand. It may
contain a "salt" to accelerate polymerization.
[0062] Examples of the transition metal salt include nickel
chloride and nickel bromide; those of the compound serving as the
ligand include triphenylphosphine and 2,2'-bipyridine; and those of
the reducing agent include zinc, magnesium and manganese. Examples
of the transition metal complex having a coordinated ligand, which
may be used in place of the transition metal salt and the compound
as the ligand, include nickel chloride bis (triphenylphosphine) and
nickel chloride (2,2'-bipyridine).
[0063] The copolymer of the first and second component is
hydrolyzed by one of the following procedures: stirring the
copolymer for 5 minutes or more, after being thrown into an
excessive quantity of water or alcohol containing a small quantity
of hydrochloric acid; reaction of the copolymer in trifluoroacetic
acid at around 80 to 120.degree. C. for around 5 to 10 hours; and
reaction of the copolymer in a solution, e.g., N-methylpyrrolidone
solution, which contains 1 to 3 times mols of lithium bromide per
mol of the sulfonic acid ester group (--SO.sub.3R) present in the
copolymer at around 80 to 150.degree. C. for around 3 to 10 hours,
and then adding hydrochloric acid to the effluent.
[0064] Examples of the sulfonated polyarylene include a polymer
represented by the general formula (3): 15
[0065] (wherein, "m:n"=0.5 to 100:95.5 to 0, preferably 0.5 to
99.999:95.5 to 0.001; and "1" is a positive integer.
[0066] The polymer electrolyte membrane 2 maybe formed by casting,
in which the sulfonated polyarylene represented by the general
formula (3), dissolved in a solvent, is extended into a film on a
base. Thickness of the dried film is normally 10 to 100 .mu.m,
preferably 20 to 80 .mu.m. The solvent may be of
N-methyl-2-pyrrolidone, and base may be of a polyethylene
terephthalate film.
[0067] For production of the polymer electrolyte membrane 2,
polyarylene ester of sulfonic acid is made into a film following
the above procedure before it is hydrolyzed, and then
hydrolyzed.
[0068] The diffusion layer 3 is composed of a carbon paper coated
with an under layer (not shown). The under layer may be of a
mixture of carbon black and polytetrafluoroethylene particles in a
ratio of 4:6 by weight.
[0069] The electrode structure as one embodiment of the present
invention, shown in FIG. 1, can work as a fuel cell by inducing a
reducing gas, e.g., hydrogen or methanol, into the electrode
catalyst layer 1 via the diffusion layer 3 on the fuel electrode
(anode) side, and an oxidizing gas, e.g., air or oxygen, into the
electrode catalyst layer 1 via the diffusion layer 3 on the oxygen
electrode (cathode) side. When the reducing gas such as hydrogen or
methanol is introduced to the electrode catalyst layer 1 on the
fuel electrode side, this structure produces proton and electron
from the reducing gas on the fuel electrode by the actions of the
catalyst in the electrode catalyst layer 1, the proton moving
towards the electrode catalyst layer 1 on the oxygen electrode side
via the polymer electrolyte membrane 2, to react with the oxidizing
gas and electron induced in the electrode catalyst layer 1 on the
oxygen electrode side and produce water by the actions of the
catalyst contained in the catalyst layer 1. Therefore, a current
can be produced by connecting the fuel electrode and oxygen
electrode to each other by a cable, to produce a circuit which
sends the electron formed on the fuel electrode towards the oxygen
electrode.
[0070] The sulfonated polyarylene for the present embodiment may be
replaced by a sulfonated polyetheretherketone (PEEK) as a less
expensive hydrocarbon-based polymer than a
perfluoroalkylenesulfonic acid compound, for the polymer
electrolyte membrane 2.
[0071] However, the polymer electrolyte membrane of sulfonated
polyetheretherketone involves problems resulting from low
durability under hydrothermal conditions, although good in gas
barrier property. Decreasing its sulfonating equivalents to
decrease its ion-exchanging capacity does improve its durability
under hydrothermal conditions. However, a polymer electrolyte
membrane of low ion-exchanging capacity naturally cannot secure a
sufficient power production capacity.
[0072] Sulfonated polyarylenes include the polymer represented by
the general formula (4), in addition to the one for the present
embodiment: 16
[0073] However, the polymer represented by the general formula (4)
involves problems resulting from very low toughness, and low
durability and handleability.
[0074] The polymer represented by the general formula (5) is still
another sulfonated polyarylene. 17
[0075] The polymer represented by the general formula (5) is
tougher than the one represented by the general formula (4), and
hence realizes a higher power production capacity. Moreover, it is
serviceable for a much longer time.
[0076] However, the polymer represented by the general formula (5)
is prepared by copolymerizing the repeating unit represented by the
general formula (6) with the repeating unit represented by the
general formula (7), and sulfonating the resulting copolymer, to
introduce the sulfonic group in a benzene ring which is not
adjacent to the electron attracting group: 18
[0077] As a result, the polymer represented by the general formula
(5) has the sulfonic group tending to leave the benzene ring.
Therefore, such a sulfonated polyarylene needs to have higher
sulfonating equivalents to secure a required ion-exchanging
capacity. However, it tends to have the sulfonic group working as
the crosslinking points under high temperature/low humidity
conditions to produce insoluble components by the inter-molecular
crosslinking reactions, increasingly as its sulfonating equivalent
level increases. As a result, it loses toughness and cannot exhibit
sufficient durability.
[0078] Next, examples of the present invention and comparative
examples are described.
EXAMPLE 1
[0079] In this example, first prepared was the sodium salt of
4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfonic acid, represented
by the general formula (8): 19
[0080] It was prepared by the following procedure. First, a 3
L-three-necked flask equipped with a stirrer and cooling tube was
charged with 137.3 g (400 mmols) of
2,5-dichloro-4'-phenoxybenzophenone, and then with 500 mL of
1,2-dichloroethane to dissolve the former, to which 56 mL of
concentrated sulfuric acid, 152 mL of acetic anhydride and a 2
mol/L acetyl sulfate solution freshly prepared from 400 mL of
1,2-dichloroethane were added with stirring. The reaction was
allowed to proceed for 3 hours in an oil bath kept at 60.degree. C.
Then, 300mL of 1-propanol was added to terminate the reaction.
Then, the reaction system was concentrated to a volume of 400 mL,
to which an aqueous NaOH solution (120 g (3 mols) of NaOH/400 mL of
water) was added. The 1,2-dichloroethane remaining in the reaction
system was removed by azeotropic distillation, the resulting
transparent light-yellowish solution was cooled, and the separated
precipitate was recovered by filtration. It was dried under a
vacuum at 70.degree. C. to prepare the fine white powder of sodium
salt of 4-[4-(2,5-dichlorobenzoyl)phenoxy]ben- zenesulfonic acid
(crude crystal) as the target.
[0081] Next, the as-received crude crystal was used without further
purification to prepare
4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfonyl chloride,
represented by the general formula (9). 20
[0082] The compound represented by the general formula (9) was
prepared by the following procedure. First, 300 mL of acetonitrile
as a solvent, 200 mL of sulfolane and then 245.3 g (1.6 mols) of
phosphoryl trichloride were added to 215 g (around 400 mmols) of
the crude crystal of sodium salt of
4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfonic acid, and the
reactions were allowed to proceed at 70.degree. C. Then, 5 mL of
N,N-dimethylacetoamide was added to the reaction system, and the
resultant yellow suspension was stirred at 71 to 73.degree. C. for
40 minutes, and cooled to 3.degree. C. Next, 1 L of cool water was
added to the reaction system at a rate to keep the reaction system
at 10.degree. C. or lower. The precipitate was collected, washed
with cool water and recrystallized with 350 mL of toluene, to
prepare 135 g of the white crystal of
[0083] 4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfonyl chloride
as the target product (melting point: 130.5 to 131.5.degree. C. in
a yield of 87% based on the sodium salt of
[0084] 4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfonic acid.
[0085] Next,
[0086] 4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfonyl chloride
was used to prepare
[0087] 4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfonic acid
iso-butyl represented by the general formula (10): 21
[0088] The compound represented by the general formula (10) was
prepared by the following procedure. First, 22.09 g (50mmols) of
4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfonyl chloride and 4.0
g (55 mmols) of 2-methyl-1-propanol were added to 30 mL of a
pyridine solvent dropwise in 40 minutes with mechanical stirring
and cooling. The resulting thick suspension was further stirred at
12 to 15.degree. C. for 1 hour. Next, the reaction system was
incorporated with 30 mL of concentrated hydrochloric acid and 100 g
of ice at a stroke, and stirred until the suspension became uniform
gradually. It was then filtered quickly by a Buchner funnel, and
the resulting white, viscous precipitate was recovered. The
resulting precipitate was redissolved in 300 mL of ethyl acetate.
The solution was washed with water by a separatory funnel, and
concentrated by distillation under a vacuum to remove the solvent,
after the organic layer was dried with magnesium sulfate. The
lightly yellowish, oily liquid, obtained by the concentration
procedure, was dissolved in 30 mL of hot hexane, and allowed to
stand in a freezer for a couple of days, to prepare the white
crystal of
[0089] 4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfonic acid
iso-butyl (melting point: 73 to 74.degree. C.) as the target
product in a yield of 70%.
[0090] Next, the oligomer represented by the general formula (11)
was prepared. 22
[0091] The oligomer represented by the general formula (11) was
prepared by the following procedure. First, a 1 L-three-necked
flask equipped with a stirrer, thermometer, cooling tube,
Dean-Stark tube and three-way cock for introducing nitrogen was
charged with 67.3 g (0.20 mols) of
2,2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane (bisphenol
AF), 60.3 g (0.24mols) 4,4'-dichlorobenzophenone, 71.9 g (0.52
mols) of potassium carbonate, 300 mL of N,N-dimethylacetamide and
150 mL of toluene, which were heated in an oil bath at 130.degree.
C. with stirring in a nitrogen atmosphere for the reactions. The
reaction process was continued while water produced and toluene
were removed via the Dean-Stark tube by azeotropic distillation.
Essentially no production of water was observed in around 3 hours.
Then, reaction temperature was gradually increased from130 to
150.degree. C., to remove most of toluene. After the reaction
process was continued at 150.degree. C. for 10 hours, 10.0 g of
4,4'-dichlorobenzophenone was added to the reaction system, and the
process was further continued for 5 hours.
[0092] The effluent solution was left to cool, and filtered to
remove inorganic precipitates as by-product. The filtrate was
thrown into 4 L of methanol. The precipitated product was separated
and recovered by filtration, dried and then dissolved in300mL of
tetrahydrofuran. It was reprecipitated in 4 L of methanol to
prepare 95 g of the oligomer represented by the general formula
(11) in a yield of 85%.
[0093] Next, the sulfonate-esterified polyarylene represented by
the general formula (12) was prepared. 23
[0094] The sulfonate-esterified polyarylene represented by the
general formula (12) was prepared by the following procedure.
First, a mixture of 15.34 g (32 mmols) of the
4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfon- ic acid iso-butyl
represented by the general formula (10), 10.52 g (1.33 mmols) of
the oligomer represented by the general formula (11)
(number-average molecular weight: 7940), 0.65 g (1 mmol) of
bis(triphenylphosphine) nickel dichloride, 33.50 g (13.33 mmols) of
triphenylphosphine, 0.65 g (4.83 mmols) of sodium iodide and 5.45 g
(83.33 mmols) of powdered zinc was incorporated with 60 mL of dried
N-methylpyrrolidone in a nitrogen atmosphere.
[0095] The reaction system was heated with stirring to 74.degree.
C., at which the reaction process was allowed to proceed for 3
hours. It showed increased viscosity during the reaction process.
The resulting polymerized solution was diluted with 250 mL of
tetrahydrofuran, stirred for30 minutes, and filtered in the
presence of celite as a filtration aid. The filtrate was poured in
a largely excessive quantity of methanol (1500 mL) for
solidification. The solidified product was separated by filtration,
dried in wind, and redissolved in a mixed solvent of
tetrahydrofuran (200 mL) and N-methylpyrrolidone (30 mL), and
solidified/separated in a largely excessive quantity of methanol
(1500 mL). It was dried in wind and then under heating, to prepare
20.54 g of the polyarylene ester of sulfonic acid represented by
the general formula (12) as the target product (yellowish, flaky
form) in a yield of 78%.
[0096] Next, 5.08 g of the polyarylene ester of sulfonic acid
represented by the general formula (12) was dissolved in 60 mL of
N-methylpyrrolidone, and heated to 90.degree. C. Then, the reaction
system was incorporated with a mixture of methanol (50 mL) and
concentrated hydrochloric acid (8 mL) at a stroke. The resulting
suspension of the reaction solution was treated under mild reflux
conditions for reaction for 10 hours, and then distilled to remove
an excessive quantity of methanol, after the distillation unit was
attached to the reaction system, to prepare a lightly green,
transparent solution of the sulfonated polyarylene represented by
the general formula (3) 24
[0097] Next, the lightly green, transparent solution was made into
a film on a glass plate by casting, immersed in water for 3 days,
and dried in wind and then dried under vacuum, to prepare the
polymer electrolyte membrane 2 with dry film thickness of 50
.mu.m.
[0098] In Example 1, platinum particles were supported by carbon
black (furnace black) having an average particle diameter of 30 nm
to prepare the catalyst particles (at a weight ratio of carbon
particle:platinum particle=1:1).
[0099] Next, the catalyst particles were uniformly dispersed in a
perfluoroalkylenesulfonic acid compound (e.g., Du Pont's Nafion
(trade name)) solution as an ion-conductive binder, to prepare the
catalyst paste (at a weight ratio of catalyst
particle:ion-conductive binder=5:7).
[0100] Next, a slurry prepared by uniformly dispersing a mixture of
carbon black and polytetrafluoroethylene (PTFE) particles (at a
weight ratio of 4:6) in ethylene glycol was spread on one side of a
carbon paper, and dried to prepare an under layer. This produced
the diffusion layer 3, composed of the carbon paper and the under
layer.
[0101] The catalyst paste was spread on the under layer of the
diffusion layer 3 so that the content of the platinum becomes 0.12
mg/cm.sup.2 by screen printing, heated at 60.degree. C. for 10
minutes and then at 120.degree. C. under a vacuum for 60 minutes,
and dried, to prepare the catalyst layer 1.
[0102] Next, the polymer electrolyte membrane 2 was placed between
the catalyst layers 1,1, and hot-pressed at 150.degree. C. and 2.5
MPa for 1 minute, to prepare the monolithic, electrode structure,
illustrated in FIG. 1.
[0103] Next, the electrode structure prepared in the present
example was aged at a cell temperature of 70.degree. C. and
humidity of 73% RH for both electrodes, and used for power
production at a cell temperature of 90.degree. C. and humidity of
0% RH for both electrodes, where current density was increased to
1.0 A/cm.sup.2 in 5 minutes after the power production was started
and then kept at this level. FIG. 2 shows temporal changes of cell
potential.
[0104] Next, the electrode structure prepared in the present
example was used for power production at a cell temperature of
85.degree. C., current density of 1.0 A/cm.sup.2, and humidity of
30% RH on the anode (fuel electrode) side and50% on the cathode
(oxygen electrode) side. FIG. 3 shows temporal changes of cell
potential.
COMPARATIVE EXAMPLE 1
[0105] The electrode structure illustrated in FIG. 1 was prepared
in Comparative Example 1 in the same manner as in Example 1, except
that the polymer electrolyte membrane 2 of a
perfluoroalkylenesulfonic acid polymer compound (e.g., Du Pont's
Nafion (trade name)) was used.
[0106] Next, the electrode structure prepared in the present
comparative example was used for power production at a cell
temperature of 90.degree. C. and humidity of 0% RH for both
electrodes, where current density was increased to 1.0 A/cm.sup.2
in 5 minutes after the power production was started and then kept
at this level. FIG. 2 shows temporal changes of cell potential.
[0107] Next, the electrode structure prepared in the present
comparative example was used for power production at a cell
temperature of 85.degree. C., current density of 1.0 A/cm.sup.2,
and humidity of 30% RH on the anode (fuel electrode) side and 50%
on the cathode (oxygen electrode) side. FIG. 3 shows temporal
changes of cell potential.
COMPARATIVE EXAMPLE 2
[0108] The electrode structure illustrated in FIG. 1 was prepared
in Comparative Example 2 in the same manner as in Example 1, except
that the polymer electrolyte membrane 2 of sulfonated
polyetheretherketone (PEEK) was used.
[0109] Next, the electrode structure prepared in the present
comparative example was used for power production at a cell
temperature of 90.degree. C. and humidity of 0% RH for both
electrodes, where current density was increased to 1.0 A/cm.sup.2
in 5 minutes after the power production was started and then kept
at this level. FIG. 2 shows temporal changes of cell potential.
COMPARATIVE EXAMPLE 3
[0110] The electrode structure illustrated in FIG. 1 was prepared
in Comparative Example 3 in the same manner as in Example 1, except
that the polymer electrolyte membrane 2 of the sulfonated
polyarylene represented by the general formula (4) was used. 25
[0111] Next, the electrode structure prepared in the present
comparative example was used for power production at a cell
temperature of 90.degree. C. and humidity of 0% RH for both
electrodes, where current density was increased to 1.0 A/cm.sup.2
in 5 minutes after the power production was started and then kept
at this level. FIG. 2 shows temporal changes of cell potential.
COMPARATIVE EXAMPLE 4
[0112] The electrode structure illustrated in FIG. 1 was prepared
in Comparative Example 4 in the same manner as in Example 1, except
that the polymer electrolyte membrane 2 of the sulfonated
polyarylene represented by the general formula (5) was used. 26
[0113] The sulfonated polyarylene represented by the general
formula (5) was prepared by the following procedure.
[0114] First, the oligomer represented by the general formula (11)
was prepared in the same manner as in Example 1. 27
[0115] Next, a flask was charged with 28.4 g (2.87 mmols) of the
oligomer represented by the general formula (11), 29.2 g (67.1
mmols) of
[0116] 2,5-dichloro-4'-(4-phenoxy)phenoxybenzophenone, 1.37 g (2.1
mmols) of bis(triophenylphosphine) nickel dichloride, 1.36 g (9.07
mmols) of sodium iodide, 7.34 g (28.0 mmols) of triphenylphosphine
and 11.0 g (168 mmols) of powdered zinc, and then substituted with
dried nitrogen. The mixture was incorporated with 130 mL of
N-methyl-2-pyrrolidone, heated to 80.degree. C., at which the
polymerization was carried out for 4 hours with stirring. Then, the
resulting polymerized solution was diluted with tetrahydrofuran,
and solidified with hydrochloric acid/methanol and recovered. The
recovered polymer was washed with methanol repeatedly, and
dissolved in tetrahydrofuran. It was purified by reprecipitation in
methanol, and separated by filtration. The resulting polymer was
dried under a vacuum, to prepare 5.07 g of the polyarylene
represented by the general formula (5') in a yield of 96%. 28
[0117] Next, 25 g of the polyarylene represented by the general
formula (5') was put in a 500 mL separable flask, to which 250 mL
of 96% sulfuric acid was added, and the mixture was stirred for 24
hours in a nitrogen atmosphere. The resulting solution was poured
into a large quantity of ion-exchanged water to precipitate the
polymer therein. The polymer was washed with water repeatedly until
the wash water reached pH 5 and dried, to prepare 29 g of the
sulfonated polyarylene represented by the general formula (5) in a
yield of 96%.
[0118] Next, the sulfonated polyarylene represented by the general
formula (5) was dissolved in N-methyl-2-pyrrolidone, to prepare a
polymer electrolyte solution. The solution was made into a film by
casting, and dried at 80.degree. C. in an oven, to prepare the
polymer electrolyte membrane 2 with a dry film thickness of 50
.mu.m.
[0119] Next, the electrode structure prepared in the present
comparative example was used for power production at a cell
temperature of 90.degree. C. and humidity of 0% RH for both
electrodes, where current density was increased to 1.0 A/cm.sup.2
in 5 minutes after the power production was started and then kept
at this level. FIG. 2 shows temporal changes of cell potential.
[0120] Next, the electrode structure prepared in the present
comparative example was used for power production at a cell
temperature of 85.degree. C., current density of 1.0 A/cm.sup.2,
and humidity of 30% RH on the anode (fuel electrode) side and 50%
on the cathode (oxygen electrode) side. FIG. 3 shows temporal
changes of cell potential.
[0121] It is apparent, as shown in FIG. 2, that the polymer
electrolyte membrane 2 of the sulfonated polyarylene represented by
the general formula 3 (prepared in Example 1) can be serviceable
for power production for a longer time even under high
temperature/low humidity conditions than any of the polymer
electrolyte membranes 2 prepared in Comparative Examples 1 to4, of
a perfluoroalkylenesulfonic acid compound, sulfonated
polyetheretherketone, or another sulfonated polyarylene represented
by the general formula (4) or (5), indicating that it has excellent
durability.
[0122] It is also apparent, as shown in FIG. 3, that the polymer
electrolyte membrane 2 of the sulfonated polyarylene represented by
the general formula 3 (prepared in Example 1) can be serviceable
for power production for a longer time also at higher temperature
than any of the polymer electrolyte membranes 2 prepared in
Comparative Examples 1 and 4, of a perfluoroalkylenesulfonic acid
compound, or another sulfonated polyarylene represented by the
general formula (5), indicating that it has excellent durability at
a higher temperature.
EXAMPLE 2
[0123] The polymer electrolyte membrane 2 (dry film thickness: 40
.mu.m, ion-exchanging capacity: 2.0 meq/g) of the sulfonated
polyarylene represented by the general formula (3) was prepared in
Example 2 in the same manner as in Example 1. Next, the electrode
structure illustrated in FIG. 1 was prepared in the same manner as
in Example 1, except that the polymer electrolyte membrane 2
prepared in Example 2 was used.
[0124] Next, the electrode structure prepared in the present
example was used for power production for 200 hours under the
conditions of temperature: 85.degree. C., service factor on the
fuel electrode side: 50%, service factor on the oxygen electrode
side: 50% and current density: 1 A/cm.sup.2. Its cell potential was
measured at the same current density. The results are given in
Table 1.
EXAMPLE 3
[0125] The electrode structure was prepared in Example 3 in the
same manner as in Example 2, except that platinum was contained at
0.3 mg/cm.sup.2.
[0126] It was measured for its cell potential in the same manner as
in Example 2. The results are given in Table 1.
EXAMPLE 4
[0127] The electrode structure was prepared in Example 4 in the
same manner as in Example 2, except that platinum was contained at
0.5 mg/cm.sup.2.
[0128] It was measured for its cell potential in the same manner as
in Example 2. The results are given in Table 1.
EXAMPLE 5
[0129] The electrode structure was prepared in Example 5 in the
same manner as in Example 2, except that platinum was contained at
0.9 mg/cm.sup.2.
[0130] It was measured for its cell potential in the same manner as
in Example 2. The results are given in Table 1.
REFERENCE EXAMPLE 1
[0131] The electrode structure was prepared in Reference Example 1
in the same manner as in Example 2, except that platinum was
contained at 0.05 mg/cm.sup.2.
[0132] It was measured for its cell potential in the same manner as
in Example 2. The results are given in Table 1.
REFERENCE EXAMPLE 2
[0133] The electrode structure was prepared in Reference Example 2
in the same manner as in Example 2, except that platinum was
contained at 1.1 mg/cm.sup.2.
[0134] It was measured for its cell potential in the same manner as
in Example 2. The results are given in Table 1.
1 TABLE 1 Average Platinum particle Cell content diameter potential
(mg/cm.sup.2) (nm) (V) Reference 0.05 30 0.30 Example 1 Example 2
0.12 30 0.54 Example 3 0.3 30 0.62 Example 4 0.5 30 0.63 Example 5
0.9 30 0.56 Reference 1.1 30 0.41 Example 2
[0135] It is apparent, as shown in Table 1, that each of the
electrode structures prepared in Examples 2 to 5, containing
platinum at 0.12 to 0.9 mg/cm.sup.2, exhibits a higher cell
potential and hence higher power production capacity than the one
prepared in Reference Example 1 containing platinum at 0.05
mg/cm.sup.2, i.e., below 0.1 mg/cm.sup.2, or the one prepared in
Reference Example 2 containing platinum at 1.1 mg/cm.sup.2, i.e.,
above 1.0 mg/cm.sup.2.
EXAMPLE 6
[0136] The electrode structure was prepared in Example 6 in the
same manner as in Example 4, except that it included the catalyst
particles with platinum particles supported by carbon black
(furnace black) having an average particle diameter of 12 nm.
[0137] Next, it was measured for its cell potential in the same
manner as in Example 2. The results are given in Table 2, which
also shows the results of the electrode structure prepared in
Example 4 again.
EXAMPLE 7
[0138] The electrode structure was prepared in Example 7 in the
same manner as in Example 4, except that it included the catalyst
particles with platinum particles supported by carbon black
(furnace black) having an average particle diameter of 95 nm.
[0139] Next, it was measured for its cell potential in the same
manner as in Example 2. The results are given in Table 2.
REFERENCE EXAMPLE 3
[0140] The electrode structure was prepared in Reference Example 3
in the same manner as in Example 4, except that it included the
catalyst particles with platinum particles supported by carbon
black (furnace black) having an average particle diameter of 5
nm.
[0141] Next, it was measured for its cell potential in the same
manner as in Example 2. The results are given in Table 2.
REFERENCE EXAMPLE 4
[0142] The electrode structure was prepared in Reference Example 4
in the same manner as in Example 4, except that it included the
catalyst particles with platinum particles supported by carbon
black (furnace black) having an average particle diameter of 120
nm.
[0143] Next, it was measured for its cell potential in the same
manner as in Example 2. The results are given in Table 2.
2 TABLE 2 Average Platinum particle Cell content diameter potential
(mg/cm.sup.2) (nm) (V) Reference 0.3 5 0.36 Example 3 Example 6 0.3
12 0.54 Example 4 0.3 30 0.62 Example 7 0.3 95 0.56 Reference 0.3
120 0.29 Example 4
[0144] It is apparent, as shown in Table 2, that each of the
electrode structures prepared in Examples 6, 4 and 7 with the
platinum particles supported by carbon black having an average
particle diameter of 12 to 95 nm exhibits a higher cell potential
and hence higher power production capacity than the one prepared in
Reference Example 3 with the platinum particles supported by carbon
black having an average particle diameter of below 10 nm, or the
one prepared in Reference Example 4 with the platinum particles
supported by carbon black having an average particle diameter of
above 100 nm.
* * * * *